Differential display analysis of cDNA fragments potentially involved in Nostoc flagelliforme response to osmotic stress

Nostoc flagelliforme is a terrestrial, highly drought-tolerant cyanobacterium. However, the molecular mechanism of its drought adaptation still remains little known. In this paper, we attempted to isolate those osmotic stress-regulated cDNA fragments by traditional differential display reverse transcriptase-polymerase chain reaction (DDRT-PCR). The PCR primers were chosen and evaluated from the reported HIP1D sequence-based primers and Ea/Es primers. The physiologically recovered samples were treated with 0.7 M sorbitol for 3 h. A total of 21 cDNA fragments were obtained by DDRT-PCR, and among them, 16 are up-regulated by osmotic stress. BlastX analyses showed that these up-regulated cDNA fragments are most related to ATPases, methyltransferases, transporters, glutathione synthase, signal transduction-associated components, and other unknown proteins. They are potentially important genes for N. flagelliforme to cope with drought stress since they are distinctly up-regulated by osmotic stress. In addition, five cDNA fragments are down-regulated by osmotic stress, such as the cDNA fragment of PSII protein. They may represent those genes involved in normal physiological processes and thus were inhibited by the osmotic stress. Taken together, the interpretation of the functional clues of these osmotic stress-responsive cDNA fragments has provided us an insight into the molecular mechanism of N. flagelliforme coping with the early phase of drought stress.